terminology and turbo questions

[JShadzi at aol.com]

The TransAm cars used a stock pulley with the cog all drilled up to reduce weight.

Javad

> I'm interested in hearing responses to this thread as
> well.  I wanted to post something about this when
> someone wrote about underdriven pulleys to reduce
> parasitic power losses.  We used to clip the vanes on
> the water pump for the same reason.  It actually takes
> quite a bit of power to drive the WP.  I don't know
> that I'd try this on an Audi though.  I wonder what
> the race teams did?  Clip the vanes or run an electic
> drive to the WP?  Anyone know what they did, although
> I don't know if it has any relevance to street driven
> Audis.
>
> Jim Accordino
>
> --- auditude at neta.com wrote:
> > JShadzi at aol.com wrote:
> > >
> > > << Also,  the psi rating of a turbo....
> > >  Is this the pressure on the turbo outlet, pushing
> > into
> > >  the intake?>>
> > >
> > > Well, turbos are not rated for psi per se, but
> > typically the actual
> > > psi output is measured in the intake manifold
> > where it counts.
> > >
> > > << Or, is this the pressure of exhaust acting on
> > the
> > >  turbo spooling fins?  >>
> > >
> > > No, that pressure is typically not measured, as
> > what is really
> > > important is in the intake manifold.
> >
> > Would it be a correct statement to say that
> > "clipping" mods done
> > to the exhaust turbine fins results in better
> > performance, due to
> > less backpressure of the exhaust getting out of the
> > motor?  At the
> > expensive of boost onset rpm (is that different from
> > "boost lag",
> > which is said to be different in Max Boost)?
> >
> > At some point, the turbo can be too small, and be a
> > restriction to
> > the output of the exhaust, right?
> >
> > I realize this is a different topic than where the
> > thread was, but it's
> > a factor too, isn't it?
> >
> > Is the backpressure created by the turbo a factor in
> > its efficiency
> > for a certain pressure?  I know that clipping
> > changes the a/r, and
> > that it makes it "act" like a larger turbo, but is
> > this simply due to
> > the decreased backpressure?  Or, does it have more
> > to do with the
> > new shape of the fins and the new angle at which the
> > exhaust
> > gases hit them?
> >
> > Thanks,
> >
> > Ken
>
>
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